#include "apue.h"
#include <fcntl.h>
#include <sys/mman.h>

#define COPYINCR (1024*1024*1024) /* 1GB */

int main(int argc, char *argv[]) {
	int fdin, fdout;
	void *src, *dst;
	size_t copysz;
	struct stat sbuf;
	off_t fsz = 0;

	if (argc != 3)
		err_quit("usage: %s <fromfile> <tofile>", argv[0]);

	if ((fdin = open(argv[1], O_RDONLY)) < 0)
		err_sys("cannot open %s for reading", argv[1]);

	if ((fdout = open(argv[2], O_RDWR | O_CREAT | O_TRUNC, FILE_MODE)) < 0)
		err_sys("cannot create %s for writing", argv[2]);

	if (fstat(fdin, &sbuf) < 0)
		err_sys("fstat error");

	if (ftruncate(fdout, sbuf.st_size) < 0)
		err_sys("ftruncate error");

	while (fsz < sbuf.st_size) {
		if ((sbuf.st_size - fsz) > COPYINCR)
			copysz = COPYINCR;
		else
			copysz = sbuf.st_size - fsz;

		if ((src = mmap(0, copysz, PROT_READ, MAP_SHARED,
						fdin, fsz)) == MAP_FAILED)
			err_sys("mmap error for input");

		if ((dst = mmap(0, copysz, PROT_READ | PROT_WRITE, MAP_SHARED,
						fdout, fsz)) == MAP_FAILED)
			err_sys("mmap error for output");

		memcpy(dst, src, copysz);
		munmap(src, copysz);
		munmap(dst, copysz);
		fsz += copysz;
	}
	
	exit(0);
}

